Portable computers of the type commonly referred to as "laptop" computers and "notebook" computers are becoming very popular They typically include a housing with a lid which is movable between open and closed positions, a display which is mounted on the lid, and a keyboard which is mounted on the housing beneath the lid, the keyboard and display being exposed when the lid is in the open position and being hidden and protected when the lid is in the closed position These systems also include a battery which serves as a source of power. If a user inadvertently closes the lid without remembering to turn off the power, the system can continue to operate and will run down the battery.
One solution to this problem is to provide a lid switch which, in response to movement of the lid to the closed position, shuts off power to the system. However, this can be disadvantageous because, if the user unintentionally bumps the lid and causes it to close, the contents of the volatile semiconductor memory in the computer will be lost, and thus the user may lose important data or program information which he or she did not wish to lose.
An alternative known approach is to respond to the close of the lid by producing an audible beep rather than shutting off power to the system. This permits the user to reopen the lid and continue operation without any loss of data or program information. Nevertheless, if the user does not hear the beep or forgets to open the lid following the beep, the battery may run down and cause the contents of the semiconductor memory to be lost.
A recently-developed microprocessor has the capability to save the status of an operating computer system, then shut off power to almost all of the system, and then enter a low power suspend state, and has the capability to exit the suspend state at a subsequent time, restore power to the system, restore the saved state of the system, and then resume operation from the point at which the system was interrupted. To date, systems using this microprocessor have effected entry to and exit from the suspend mode based on a manually operable push-button switch or on other internal criteria such as expiration of a timer. In these known computer systems, closing of the lid during system operation results only in generation of an audible beep, with the same disadvantages mentioned above.
An object of the invention is therefore to provide an arrangement for causing a system to enter and subsequently exit suspend mode in response to closing and subsequent opening of a lid.